Hello, this is Emily.
Do you still have access to that computer? If so, go ahead and sign in. Then do the following:
Go to Settings > Accounts > Your info
Click on Sign in with local user instead. follow the steps and finish the rest.
(If you don't see the "sign in with a local account instead option, click on "Stop signing into Microsoft apps automatically" first, then relaunch this page. )
Restart the computer (Do Not skip)
That should remove your Micosoft account, and turn the Windows sign in user into a local user instead.